The present invention relates to an apparatus for processing color picture information signals for use in a color copier using an image sensor with a plurality of light receiving elements assigned for each picture element.
Conventional color copying technology involves two categories: an electronic color picture reproduction system and a chemical color picture reproduction system. The former uses, for color picture reproduction, electrical signals obtained by optically scanning a color original picture. The latter employs a chemical process, such as development process for color picture reproduction.
The electrical color picture reproduction system is, at the present stage of technology, liable to be adversely affected with noises and is low in resolution, although having attractive advantages of no need for chemical process and of possibility of various processings for the color image reproduction.
With this electrical reproduction system, to obtain three color signals for reproducing a color picture, there are needed at least three color filter elements with different spectral characteristics for each pixel.
The following systems, each of which employs a light receiving element array such as a CCD (charge coupled device) array to obtain three color signals for each pixel, have been known.
(1) According to a first system, one light receiving element is assigned to one pixel. Three-color light sources or three color filters provided for one pixel are sequentially switched to provide three color signals for each pixel on a time division basis.
(2) According to a second system, a spatially dividing type image sensor is used in which three light receiving elements are assigned for one pixel. The three light receiving elements are respectively provided with different color filters, to provide three color signals.
The second system is disadvantageous over the first system in that three times as many as light receiving elements are required and that the three color signals for one pixel are not exactly representative of picture information at a point on the original picture. Conversely, the second system has no need of a moving device to switch the light sources or the color filters, resulting in high-speed readout of picture information. Owing to this feature, the second system has predominantly been employed for picture information reproduction.
Strictly speaking, in the color copier using the spatially dividing type image sensor the color signals corresponding to one pixel are color signals corresponding to separate points on the color picture. In a picture portion where variation in brightness is small an influence imposed by the spatially dividing type image sensor on a reproduced color picture is negligibly small due to deterioration of high frequency components cause by a distributed index rod lens array. In picture portions where luminance greatly varies, such as edges in a black character picture, however, unnegligible errors occur in signals during color signal processing. Such errors also occur in a chromatic edge portion and a dot picture (color picture printed by printing machines). This causes deterioration in color reproducibility and picture quality of a reproduced color picture.